It sounds to me that your SO is carrying around a significant amount of emotional baggage from his own upbringing, and his denial of DD's abilities is largely a defensive mechanism... he's protecting himself from reliving those old memories, while desperately hoping she'll be spared from a similar experience.
After all, this made me channel my inner Doctor Phil:
He says he was happy in school where he could play with his friends and daydream all day long and relax.
As Dr. Phil would say, "How'd that work out for you?"
He never finished high school and never found a career.
I think he needs to take a step back and maybe get some counseling on his own issues, because what he's doing right now is projecting those issues onto his DD, and this can be extremely harmful to her. If he's always deprecating her abilities, she's going to doubt her abilities. Gifted girls have enough problems with this sort of thing without Dad becoming a part of the problem.
I think for the sake of family peace and harmony, we should both agree to neither push nor prevent and let DD be who she wants to be regardless of our own priorities and agenda.
I think that if anyone is looking for one simple, universal rule of parenting, regardless of the child's unique combination of personality/abilities/challenges, this will do.
